Steel frame structures such as buildings and the like are typically constructed with a welded connection between the beams and columns. While this welded connection is typically satisfactory under most normal loading conditions, it has been found to be inadequate under excessive and abnormal loading conditions such as those that occur during earthquakes. The high loading forces placed on the welded beam/column connections during earthquakes are oftentimes sufficient to fracture or otherwise damage the welded connections leading to premature loss of structural integrity. Typically, welding has been relied upon as the method for repairing these damaged welds. The repair can be in the form of a simple reweld or can involve a more elaborate and more expensive welding scheme. However, these approaches to repairing welded connection joints are inadequate and fraught with a variety of disadvantages and drawbacks.
In one respect, welding the damaged joint connection between a beam and a column in an existing building presents the danger of fires since welding gives off a significant amount of heat. In addition, if this occurs, the automatic sprinkler systems in the building can be set off. The result to the existing building is not only fire damage, but water damage as well.
In addition, welding the damaged connection joint provides a rather limited range of structural performance in a variety of contexts such as plastic rotational capacity. Also, the repair of the damaged connection can be somewhat time consuming, can create highly objectionable fumes, and can otherwise cause disturbance to the tenants in the occupied structures. Further, in the context of rewelds, the weld that is applied to repair the damaged connection joint may not be any more reliable than the welded connection joint in existence prior to the damage. Thus, it is likely that the repaired connection joint will be susceptible to the same damage causing forces as the original welded connection.
The damage caused by earthquakes has led at least one city to enact an ordinance requiring the inspection of a large number of steel moment frame buildings for purposes of identifying inadequate constructions. This inspection has revealed cracked welds in the buildings not necessarily attributable to earthquake damage, but rather the result of poor construction. While this non-earthquake related damage may not affect the structural integrity and viability of the buildings at the present time, the buildings are certainly more readily susceptible of damage during future earthquakes. Thus, the ordinance requires that the buildings be repaired which, in accordance with current practices, means that the damaged joint must be rewelded.
In view of the foregoing, a need exists for facilitating the repair of damaged buildings, including those resulting from earthquakes and those which simply have been poorly constructed. More particularly, a need exists for a way of repairing damaged weld connections between beams and columns in a steel frame structure that is not susceptible of the same disadvantages and drawbacks associated with rewelding the existing damaged weld joint.
One type of beam/column connection that has been proposed in the past is disclosed in U.S. Pat. No. 3,938,297 to Sato et al. The connection involves a T-shaped member that is used to provide a bolted connection between the beam and the column. While this type of connecting member possesses the ability to be used in the context of new building constructions, it is not at all suited for use in repairing damaged beam/column weld connections in a steel moment frame building. That is because the configuration and construction of the connecting member does not lend itself to being placed at an existing beam/column interface. Rather, the construction of the connecting member is such that in order to utilize it in the context of repairing an existing weld, the existing weld would have to be torched and completely removed to separate the beam from the column. In addition, it would likely be necessary to remove a portion of the beam so that the connecting element can be fitted in place. As can be appreciated, this does not really represent a viable solution to the repair of damaged buildings. Indeed, it would be much easier to simply reweld the damaged weld joint.
A need exists, therefore, for a way of repairing a damaged weld connection between a beam and a column through use of a bolted connection. It would also be preferable if the solution was also adaptable for use in connection with the construction of new steel frame structures to thereby provide a rigid moment connection having a wide range of uses.